Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N1/00—Silencing apparatus characterised by method of silencing
  • F01N1/003—Silencing apparatus characterised by method of silencing by using dead chambers communicating with gas flow passages
  • F01N1/006—Silencing apparatus characterised by method of silencing by using dead chambers communicating with gas flow passages comprising at least one perforated tube extending from inlet to outlet of the silencer
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N1/00—Silencing apparatus characterised by method of silencing
  • F01N1/02—Silencing apparatus characterised by method of silencing by using resonance
  • F01N1/026—Annular resonance chambers arranged concentrically to an exhaust passage and communicating with it, e.g. via at least one opening in the exhaust passage
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
  • F01N13/02—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate silencers in series
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
  • F02M35/00—Combustion-air cleaners, air intakes, intake silencers, or induction systems specially adapted for, or arranged on, internal-combustion engines
  • F02M35/12—Intake silencers ; Sound modulation, transmission or amplification
  • F02M35/1205—Flow throttling or guiding
  • F02M35/1216—Flow throttling or guiding by using a plurality of holes, slits, protrusions, perforations, ribs or the like; Surface structures; Turbulence generators
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
  • F02M35/00—Combustion-air cleaners, air intakes, intake silencers, or induction systems specially adapted for, or arranged on, internal-combustion engines
  • F02M35/12—Intake silencers ; Sound modulation, transmission or amplification
  • F02M35/1255—Intake silencers ; Sound modulation, transmission or amplification using resonance
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
  • F24F13/00—Details common to, or for air-conditioning, air-humidification, ventilation or use of air currents for screening
  • F24F13/24—Means for preventing or suppressing noise
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/161—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general in systems with fluid flow
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N2470/00—Structure or shape of gas passages, pipes or tubes
  • F01N2470/02—Tubes being perforated
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N2470/00—Structure or shape of gas passages, pipes or tubes
  • F01N2470/24—Concentric tubes or tubes being concentric to housing, e.g. telescopically assembled
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N2490/00—Structure, disposition or shape of gas-chambers
  • F01N2490/15—Plurality of resonance or dead chambers
  • F01N2490/155—Plurality of resonance or dead chambers being disposed one after the other in flow direction
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
  • F24F13/00—Details common to, or for air-conditioning, air-humidification, ventilation or use of air currents for screening
  • F24F13/24—Means for preventing or suppressing noise
  • F24F2013/245—Means for preventing or suppressing noise using resonance

Definitions

• the provided articles and methods relate to reducing noise associated with a flow system.
• Elimination or reduction of sound energy at its source is preferred, but not always possible.
• airborne sound energy derives from the rapid expansion of internal combustion engine chamber exhaust gases. As these combustion gases are exhausted, a sound wave front travels at sonic velocities through the exhaust system. Automotive noise can also come from cooling fans, alternators and other engine accessories. Accordingly, manufacturers have turned to acoustic technologies capable of substantially reducing the noise emitted by these devices.
• the nature of the noise to be reduced is of considerable significance in developing an efficient exhaust or HVAC silencer.
• the airborne sound energy from a combustion engine or HVAC system typically comes of a plurality of sources, each emitting sound over its own characteristic frequencies.
• attenuation of a sound wave can be accomplished by causing the wave to encounter surfaces or structures that cause acoustic energy to be dissipated or diverted away from sensitive locations; these interactions turn the individual wave components of high amplitude into a plurality of waves of lesser amplitude, thus lowering the overall noise level.
• Such devices, to be efficient may comprise a series of component devices that are individually tuned to alter the phase relationships of respective sound waves.
• perforated films can be used to attenuate sound energy in acoustic silencers.
• the devices described in these disclosures are generally used for static flow and do not address the effect of such perforated films on the pressure drop associated with the device, as addressed below.
• Pressure drop is an often unappreciated problem in acoustic management. As used herein, this is the difference in air pressure measured between the inlet and outlet ends of an inline acoustic device.
• a high pressure drop is often the result of poor flow characteristics in the silencer, which can in turn lead to excessive heat and inefficient device performance. For example, in high performance vehicles, a high pressure drop in the exhaust system can lead to reduced horsepower and torque. Similarly, in an HVAC system, a high pressure drop forces the fans driving the air to work harder, resulting in high power expenditure. Aspects of the silencer that improve acoustic attenuation generally tend to increase pressure drop, and vice versa, so the technical solution has often been viewed as a tradeoff between these two considerations.
• the provided acoustic devices address the dual problems of acoustic attenuation and pressure drop by incorporating one or more perforated films into the air flow field of an expansion chamber.
• Use of the perforated film enabled these devices to obtain significant sound attenuation by attenuating the pressure waves over a wide target frequency range spanning the human speech range of 250 Hz to 4000 Hz. Further, these devices facilitate air flow through the expansion chamber, thereby improving flow performance relative to those of conventional devices that do not include the perforated films.
• an acoustic device has an inlet and an outlet comprising: an external housing defining an expansion chamber; and a tubular wall extending through and partitioning the expansion chamber into a central chamber and a peripheral chamber adjacent the central chamber, wherein both the inlet and outlet communicate with the central chamber, and wherein the tubular wall includes a plurality of apertures formed therethrough to allow air flow between the central and peripheral chambers, the plurality of apertures configured to provide an average flow resistance ranging from 100 MKS Rayls to 5000 MKS Rayls.
• a method of attenuating airborne sound energy using an acoustic device with an external housing defining an expansion chamber, a tubular wall extending through and partitioning the expansion chamber into a central chamber and peripheral chamber adjacent the central chamber, and an inlet and outlet communicating with opposing ends of the central chamber comprising: flowing air through the central chamber; and directing the sound energy from the central chamber through a plurality of apertures disposed in the tubular wall, wherein the plurality of apertures provide an average flow resistance ranging from 100 MKS Rayls to 5000 MKS Ray Is.
• FIG. 1 is a front, elevational view of an acoustic device according to one exemplary embodiment
• FIG. 2 is a side, cross-sectional view of the acoustic device of FIG. 1;
• FIG. 3 is a front, elevational view of an acoustic device according to another exemplary embodiment
• FIG. 4 is a side, cross-sectional view of the acoustic device of FIG. 3;
• FIGS. 5A-5D are perspective views of further exemplary configurations of an acoustic device.
• FIG. 6 is a spectrum plot of transmission loss (in decibels) versus frequency (in
• FIG. 7 is a spectrum plot of transmission loss (in decibels) versus frequency (in Hertz) for various acoustic devices having a dual expansion chamber.
• FIG. 8 is a plot comparing air pressure drop (pascals) versus flow rate (liters per minute) for various acoustic devices having a single expansion chamber.
• the terms "preferred” and “preferably” refer to embodiments described herein that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.
• FIGS. 1 and 2 An exemplary acoustic device is illustrated in FIGS. 1 and 2 and herein designated by the numeral 100.
• the acoustic device 100 has an external housing 102 that is generally hollow and has rigid walls.
• the external housing 102 is cylindrical.
• the shape of the external housing 102 may assume any of a number of geometric shapes, including a cuboid, elliptical prism, or cone.
• the external housing 102 may be provided as a single, unitary component or comprise two or more parts that are coupled together. If desired, the external housing 102 can be made by joining two halves or sections along an interface extending along the length of the acoustic device 100.
• the interior surfaces of the hollow external housing 102 define an expansion chamber 104.
• the expansion chamber 104 is connected to both an inlet 106 and an outlet 108, through which air can flow into and out of the acoustic device 100, respectively.
• the inlet 106 and outlet 108 may have the same or different diameters.
• the expansion chamber 104 by its nature, has a cross-sectional area significantly larger than the cross-sectional area of the inlet 106. As depicted, the cross-sectional area of the expansion chamber 104 is also larger than that of the outlet 108, which has a similar diameter as the inlet 106. In FIGS. 1-2, the expansion chamber 104 has a uniform cross- section, although expansion chambers in alternative configurations may have cross-section dimensions that deviate in size or shape from that illustrated here.
• the expansion chamber 104 is a quarter-wave resonator.
• a quarter-wave resonator is an enclosure in which a propagating sound wave can enter at one end and reflect off a rigid boundary at the opposite end in a manner that produces a standing wave. This occurs when the phases of reflected compressions and rarefactions at the inlet of the expansion chamber 104 coincide exactly with the vibration of the sound source, a condition referred to as resonance. At resonance, there is optimized scattering and/or absorption of the sound waves by the expansion chamber 104. Multiple expansion chambers that resonate at different frequencies can be connected in series to reduce noise over a broad frequency range.
• the acoustic device 100 further includes a tubular wall 110 that has a cylindrical shape and extends along the longitudinal axis of the expansion chamber 104.
• the diameter of the tubular wall 110 essentially matches that of the inlet 106 and outlet 108. This is, however, not critical, and the cross- sectional areas of the inlet 106, outlet 108, and tubular wall 110 need not be identical. Further, the inlet 106, outlet 108, and tubular wall 110 could either be aligned with or offset from the central, longitudinal axis of the expansion chamber 104.
• the tubular wall 110 need not be cylindrical and other shapes such as a conical or square duct would also function acoustically.
• the tubular wall 110 divides the expansion chamber 104 into two chambers that extend along the full length of the expansion chamber 104— a central chamber 1 12 and a peripheral chamber 114.
• the central chamber 112 is the cylindrical space bounded within the inner surface of the tubular wall 110.
• the distal ends of the central chamber 112 are longitudinally aligned with both the inlet 106 and outlet 108 such that the central chamber 112 freely communicates with each.
• the peripheral chamber 114 is the portion of the expansion chamber 104 located outside of the central chamber 112. In this embodiment, the peripheral chamber 114 assumes the shape of a cylindrical shell that is concentric with the central chamber 112.
• tubular wall 110 extends across the overall length of the expansion chamber 104 here, it is also possible for the tubular wall 110 to extend along only a portion of the overall length of expansion chamber 104. In such cases, the central chamber 112 would be bounded by the terminal end of the tubular wall 110 within the external housing 102, with the peripheral chamber 114 occupying the balance of the expansion chamber 104.
• the spacing between the terminal end of the tubular wall 110 and the outlet end of the expansion chamber 104 can be advantageously tuned to attenuate preferentially sounds of particular frequencies.
• This acoustic device 100 could also function if peripheral chamber 114 is subdivided in the axial direction to create cells, segments, or compartments adjacent to the tubular wall 110. Consequently, there need not be a continuously connected chamber adjacent to the tubular wall 110.
• the walls that represent the boundaries of such compartments can be either solid or perforated. In some embodiments, there are only partial walls between these compartments.
• the tubular wall 110 can extend along at least 50 percent, at least 60 percent, at least 70 percent, at least 80 percent, or at least 90 percent of the overall length of the expansion chamber 104. Moreover, the tubular wall 110 can extend along at most 99 percent, at most 95 percent, at most 80 percent, at most 70 percent, or at most 60 percent of the overall length of the expansion chamber 104.
• the external housing 102 and the tubular wall 110 may be made of any structurally suitable material. In ambient temperature applications, including most HVAC applications, these components are advantageously made from polymeric materials, which can be lighter and cleaner than their metal counterparts.
• Preferred polymeric materials include thermoplastics and thermosets suitable for injection molding, extrusion, blow molding, rotomolding, reactive injection molding, and compression molding.
• Particularly suitable thermopolymers include, for example, ABS, nylon, polyethylene, polypropylene, and polystyrene. It is noted that the stiffness of the material selected can also affect the acoustic performance of the overall device, an aspect that shall be described later.
• the thickness of the tubular wall 110 has a direct bearing on the length of the apertures disposed therein.
• the tubular wall 110 has a thickness of at least 50 micrometers, at least 60 micrometers, at least 75 micrometers, at least 100 micrometers, or at least 150 micrometers.
• the tubular wall 110 has a thickness of at most 625 micrometers, at most 600 micrometers, at most 575 micrometers, at most 550 micrometers, or at most 500 micrometers.
• the tubular wall 110 is perforated along some or all of its length.
• the tubular wall 110 includes a plurality of apertures 116 (i.e. through-holes) that allow air to flow between the central chamber 114 and peripheral chamber 114.
• the apertures 116 define approximately cylindrical plugs of air that are mass components within a resonant system. These mass components vibrate within the apertures 116 and dissipate sound energy as a result of friction between the plugs of air and the walls of the apertures 116. Some dissipation also occurs as a result of destructive interference at the entrance of the apertures 116 from sound reflected in the peripheral chamber 114.
• the apertures 116 can be advantageously tuned by adjusting their arrangement (e.g. numbers and spacing) and dimensions (e.g. aperture diameter, shape and length), to obtain a desired acoustic performance over a given frequency range while minimizing the pressure drop between the inlet 106 and outlet 108.
• Acoustic performance is commonly measured, for example, by transmission loss through the acoustic device 100, which is defined here as the accumulated decrease in acoustic intensity as an acoustic pressure wave propagates from the inlet 106 to the outlet 108.
• the apertures 116 are disposed along the entire length of the tubular wall 110, the lengthwise dimension defined as the direction of air flow through the tubular wall 110.
• the apertures 116 can be disposed along only some of this length. It is preferred that the apertures 116 are disposed along at least 15 percent, at least 20 percent, at least 30 percent, at least 40 percent, at least 50 percent, at least 60 percent, at least 70 percent, at least 80 percent, at least 85 percent, at least 90 percent, or at least 95 percent of the overall length of the tubular wall 110.
• the tubular wall 110 could be only partially perforated— that is, perforated in some areas but not others. For example, there could be unperforated sections in the vicinity of the inlet or outlet here.
• the perforated areas could also extend along longitudinal directions and be adjacent to one or more non-perforated areas— for example, the tubular wall could have a rectangular cross- section tube with only one or two sides perforated.
• the apertures 116 can have a wide range of geometries and dimensions and may be produced by any of a variety of cutting or punching operations.
• the cross-section of the apertures 116 can be, for example, circular, square, or hexagonal.
• the apertures 116 are represented by an array of elongated slits. While the apertures 116 in FIG. 2 have diameters that are uniform along their length, it is possible to use apertures that have the shape of a truncated cone or otherwise have side walls tapered along at least some their length.
• Various aperture configurations are described in U.S. Patent No. 6,617,002 (Wood).
• the apertures 116 have a generally uniform spacing with respect to each other. If so, the apertures 1 16 may be arranged in a two- dimensional box pattern or staggered pattern. The apertures 116 could also be disposed on the tubular wall 110 in a randomized configuration where the exact spacing between neighboring apertures is non-uniform but the apertures 116 are nonetheless evenly distributed across the tubular wall 110 on a macroscopic scale.
• the apertures 116 are of essentially uniform diameter along the tubular wall 110.
• the apertures 116 could have some distribution of diameters.
• the average narrowest diameter of the apertures 116 is at least 10 micrometers, at least 15 micrometers, at least 20 micrometers, at least 25 micrometers, or at least 30 micrometers.
• the average narrowest diameter of the apertures 116 is preferably at most 300 micrometers, at most 250 micrometers, at most 200 micrometers, at most 175 micrometers, or at most 150 micrometers.
• the diameter of non- circular holes is defined herein as the diameter of a circle having the equivalent area as the non-circular hole in plan view.
• the perforated tubular wall 110 has a specific acoustic impedance, which is the ratio (in frequency space) of the pressure differences across the tubular wall and the effective velocity approaching that surface.
• the velocity derives from air moving into and out of the holes.
• motion of the wall can contribute to the calculation.
• Specific acoustic impedance generally varies as a function of frequency and is a complex number, which reflects the fact that pressure and velocity waves can be out of phase.
• Rayl is equal to 1 pascal-second per meter (Pa-s-m 1 ), or equivalently, 1 newton-second per cubic meter (N-s-m -3 ), or alternatively, 1 kg-s _1 -m ⁇ 2 .
• the plurality of apertures 116 in the acoustic device 100 are preferably sized to achieve significant acoustic attenuation over the speech frequency range extending approximately from 250 Hz to 4000 Hz.
• the perforated tubular wall 110 of the acoustic device 100 can be characterized by measuring its transfer impedance.
• transfer impedance is the difference between the acoustic impedance on the incident side of the film and the acoustic impedance one would observe if the film were not present—that is, the acoustic impedance of the air cavity alone.
• the apertures 116 are sized to provide an acoustic transfer impedance having a real component of at least 100 Rayls, at least 200 Rayls, at least 250 Rayls, at least 300 Rayls, at least 325 Rayls, or at least 350 Rayls.
• the plurality of apertures 116 can be sized to provide an acoustic transfer impedance having a real component of at most 5000 Rayls, at most 4000 Rayls, at most 3000 Rayls, at most 2000 Rayls, at most 1500 Rayls, at most 1400 Rayls, at most 1250 Rayls, at most 1100 Rayls, or at most 1000 Rayls (all in MKS Rayls).
• the flow resistance is the low frequency limit of the transfer impedance. Experimentally, this can be estimated by blowing a known, small velocity of air at the perforated tubular wall 110 and measuring the pressure drop associated therewith. The flow resistance can be determined as the measured pressure drop divided by the velocity.
• the flow resistance through the tubular wall 110 is at least 50 Rayl, at least 100 Rayl, at least 250 Rayl, at least 500 Rayl, or at least 1000 Rayl.
• the flow resistance can be at most 5000 Rayl, at most 3000 Rayl, at most 2000 Rayl, at most 1500 Rayl, at most 1000 Rayl, or at most 800 Rayl (all in MKS Rayls).
• the porosity of the tubular wall 110 is a dimensionless quantity representing the fraction of a given volume not occupied by solid structure.
• the apertures 116 can be assumed to be cylindrical, in which case porosity is well approximated by the percentage of the surface area of the tubular wall 110 displaced by the apertures 116 in plan view.
• the tubular wall 110 has a porosity of at least 0.3 percent, at least 0.5 percent, at least 1 percent, at least 3 percent, or at least 4 percent. On the upper end, the tubular wall 110 could have a porosity of at most 5 percent, at most 4 percent, at most 3.5 percent, at most 3 percent, or at most 2 percent.
• the tubular wall 110 is preferably made from a material having a modulus suitably tuned to vibrate in response to incident sound waves of relevant frequencies. Along with the vibrations of the air plugs within the apertures 116, local vibrations of the tubular wall 110 itself can dissipate sound energy and enhance transmission loss through the acoustic device 100. The modulus, or stiffness, of the tubular wall 110 also directly affects its acoustic transfer impedance.
• the tubular wall comprises a material having a modulus of at least 0.2 gigapascals, and/or a modulus of at most 10 gigapascals, at most 7 gigapascals, at most 5 gigapascals, or at most 4 gigapascals.
• the provided acoustic device 100 enables a sound pressure wave arriving from the inlet 106 to expand into the expansion chamber 104 without significantly interrupting mass flow through the central chamber 112.
• the acoustic device 100 decouples the technical challenge of moving air through the acoustic device 100 and allowing the pressure waves to dissipate.
• a primary advantage of the provided acoustic device 100 is its ability to reduce airborne noise while minimizing the pressure drop through the device. This effect can be measured, for example, with respect to a control acoustic device having an expansion chamber 102 devoid of the perforated tubular wall 110.
• disposing the plurality of apertures 116 on the tubular wall 110 reduces pressure drop at a benchmark flow rate of 170 liters per minute by least 20 percent, at least 35 percent, at least 50 percent, at least 60 percent, or at least 70 percent, relative to the pressure drop associated with the expansion chamber 104 alone (i.e., with the tubular wall 110 removed).
• FIG. 3 shows an acoustic device 200 having an inlet 206 and outlet 208 according to another exemplary embodiment that bears similarity to the acoustic device 100 in most respects but further includes a second peripheral chamber 218.
• a central chamber 212, a first peripheral chamber 214, and the second peripheral chamber 218 are bounded by progressively larger concentric, cylindrical outer surfaces.
• the central chamber 212 is defined by a first tubular wall 210 perforated by a plurality of apertures 216 and is geometrically aligned with the inlet 206 and outlet 208.
• the second peripheral chamber 218 is a cylindrical shell adjacent the first peripheral chamber 214. Disposed between the first and second peripheral chambers 214, 218 is a second tubular wall 220 that defines the outer boundary of the first peripheral chamber 214 and the inner boundary of the second peripheral chamber 218. Like the first tubular wall 210, the second tubular wall 220 is perforated by a plurality of second apertures 222. The second apertures 222, which allow limited communication between the first and second peripheral chambers 214, 218, operate to dissipate sound energy in a manner like that of the first apertures 216.
• the second apertures 222 may or may not be tuned to the same acoustic properties as the apertures 216.
• the apertures 222 have the same or similar acoustic transfer impedance, flow resistance, and/or porosity as the apertures 216.
• the apertures 222 can have an acoustic transfer impedance significantly higher or lower than that of the apertures 216, depending on the noise source.
• the apertures 222 can have an acoustic transfer impedance that is lower than that of the apertures 216 by 50 Rayls, by 100 Rayls, by 150 Rayls, by 200 Rayls, by 300 Rayls, by 400 Rayls, or by 500 Rayls. Conversely, the apertures 222 can have an acoustic transfer impedance that is greater than that of the apertures 216 by 50 Rayls, by 100 Rayls, by 150 Rayls, by 200 Rayls, by 300 Rayls, by 400 Rayls, or by 500 Rayls (all in MKS Rayls).
• the attenuation of sound provided by the acoustic device 200 was enhanced relative to that of the acoustic device 100, the addition of the second tubular wall 220 and second peripheral chamber 218 was not found to significantly increase pressure drop across the expansion chamber. This is a major technical benefit, because the apertures 222 can be specifically tuned to dissipate particular sound frequencies without a significant increase in pressure drop.
• Remaining aspects of the acoustic device 200 are analogous to those of acoustic device 100 as already shown in FIGS. 1 and 2 and are not examined here.
• peripheral chambers may be included in the provided acoustic devices having structural features analogous to the peripheral chambers 114, 214, 218 described herein.
• FIGS. 5A-5D A series of dual-chamber acoustic devices are shown in FIGS. 5A-5D.
• an additional expansion chamber has been incorporated into the acoustic device.
• FIG. 5A shows an acoustic device 300 that has the same overall length as the acoustic devices 100,200, but includes a pair of expansion chambers 304, 304, each being less than half the length of the expansion chamber 104, 204.
• FIGS. 5B and 5C show acoustic devices 400, 500 having respective expansion chambers 404, 504 that are asymmetric. In the acoustic device 400, the expansion chamber 404 adjacent the inlet is longer; in the acoustic device 500, the expansion chamber 504 adjacent the outlet is longer.
• FIG. 5D shows an acoustic device 600 having expansion chambers 604 that have the same size but are shorter and separated from each other by a greater distance. Each of these devices is tuned to attenuate noise over a different acous
• additional expansion chambers may be added (a third, fourth, etc.) to further attenuate sound energy over specific frequency ranges. Further, the separation between adjacent chambers may be reduced to zero, in which case the peripheral chamber is simply segmented into a number of annular segments along its length.
• An acoustic device having an inlet and an outlet comprising: an external housing defining an expansion chamber; and a tubular wall extending through and partitioning the expansion chamber into a central chamber and a peripheral chamber adjacent the central chamber, wherein both the inlet and outlet communicate with the central chamber, and wherein the tubular wall includes a plurality of apertures formed therethrough to allow air flow between the central and peripheral chambers, the plurality of apertures configured to provide an average flow resistance ranging from 100 MKS Rayls to 5000 MKS Rayls.
• tubular wall comprises a material having a modulus ranging from 0.2 GPa to 10 GPa.
• tubular wall comprises a material having a modulus ranging from 0.2 GPa to 5 GPa.
• tubular wall comprises a material having a modulus ranging from 0.2 GPa to 4 GPa.
• the tubular wall is a first tubular wall
• the apertures are first apertures
• the peripheral chamber is a first peripheral chamber and further comprising: a second tubular wall defining a second peripheral chamber adjacent the first peripheral chamber, wherein the second tubular wall has a plurality of second apertures sized to provide an acoustic transfer impedance significantly lower than that of the plurality of first apertures.
• any one of embodiments 30-33 wherein the wall is a first wall, the apertures are first apertures, and the peripheral chamber is a first peripheral chamber and further comprising: directing the sound energy from the first peripheral chamber through a plurality of second apertures disposed in a second wall bounding the first peripheral chamber into a second peripheral chamber adjacent the first peripheral chamber to provide a transfer impedance for the second wall that is significantly lower than that of the first wall.
• the acoustic properties of a microperforated film or panel can be measured by following the procedures outlined in ASTM E2611 - 09 (Standard Test Method for Measurement of Normal Incidence Sound Transmission of Acoustical Materials Based on the Transfer Matrix Method). The data collected from this procedure can be used to obtain the acoustic transmission loss.
• This data can also be used to obtain the transfer impedance of the film.
• One of the outputs of this procedure is a 2 x 2 transfer matrix that relates the pressure and acoustic particle velocity on the two sides of the microperforated film.
• the elements of the transfer matrix can then be used to calculate the transfer impedance of the film.
• Equation (1) p l and v l can be written in following forms:
• a separate acoustic device was assembled without any perforated film and without a housing to form a chamber. Only one end cap was used, and this measurement served as a baseline air flow measurement without any chambers or film. This baseline measurement was then subtracted from each measurement shown in FIG. 8, so that the pressure drop curves shown represent the pressure drop increase relative to the baseline.
• FIGS. 1 and 2 An acoustic device schematically shown in FIGS. 1 and 2 was assembled using the following procedure and materials.
• a cylindrical external housing defining a chamber was prepared via rapid prototyping (Fortus 400 model 3D printer, Stratasys Ltd., Eden Prairie, MN) using black acrylonitrile-butadiene-styrene (ABS) resin (Stratasys Ltd., Eden Prairie, MN).
• the length of the chamber was 9.6 cm.
• the inner diameter and outer diameter of the housing were 2.9 cm and 15.2 cm, respectively.
• End caps for the chamber were also prepared separately using rapid prototyping and black ABS resin.
• the end caps contained a 2.9 cm diameter annulus through which system air can flow through the acoustic device. Annular grooves were incorporated into the design of the end caps to contain tubes of perforated film.
• a perforated film was prepared as described in U.S. Patent No. 6,617,002 (Wood).
• a film-grade polypropylene resin was used to extrude the film.
• the film was perforated after extrusion by embossing the film and then heat treating the embossments to create apertures.
• the resulting film had a thickness of 0.35 mm, a basis weight of approximately 400 grams/meter 2 and an aperture/perforation density of 111 apertures/cm 2 with each individual aperture being roughly circular in shape with a diameter of approximately 0.094 mm.
• Flow resistance was determined to be approximately 450 MKS Rayls.
• An open ended tube was prepared from the perforated film, the tube having a length of 9.7 cm and a diameter of 2.9 cm. The tube was then inserted into the housing and the annular grooves within the end cap forming a central chamber 112 and a peripheral chamber 114.
• Example 2 An acoustic device was assembled as in Example 1 above without any perforated film, representing a simple expansion chamber.
• Example 2 An acoustic device was assembled as in Example 1 above.
• the resulting film had a thickness of 0.35 mm, a basis weight of approximately 400 grams/meter 2 and an aperture density of 46 apertures/cm 2 , the average aperture diameter being approximately 0.077 mm.
• the effective aperture diameter was decreased as compared to Example 1 to produce a film with a static air flow resistance of approximately 1750 MKS Rayls.
• Pressure drop data on this device are provided in FIG. 8, as indicated.
• An acoustic device was assembled as in Example 1 above except two separate tubes of different diameters were created from the perforated film to provide the configuration shown in FIG. 4.
• the tubes were inserted into the housing and the annular grooves within the end cap forming the central chamber 212 and first and second peripheral chambers 214, 218.
• the two concentric tubes were spaced approximately 2.8 cm apart from each other along radial directions.
• An acoustic device was assembled as in Example 1 above except two separate chambers in series were used, shown schematically in FIG. 5C (with air flowing from left to right). The two chambers were in fluid communication with each other, and spaced apart by a gap of approximately 2 cm.
• An acoustic device was assembled as in Example 4 above except without any perforated film.
• Example 3 An acoustic device was assembled as in Example 3 above except two separate chambers in in series were used as shown in Example 4. The two chambers were spaced apart from each other by a gap of approximately 2 cm.
• each chamber contained a pair of concentric tubes with different diameters created from the perforated film, with the larger of the concentric tubes spaced approximately 2.8 cm apart from the smaller one along radial directions.
• Example 2 An acoustic device was assembled as in Example 1 , except a solid, non-perforated film was substituted for the perforated film.
• Pressure drop data on this device are provided in FIG. 8, as indicated.

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• 2015
  • 2015-09-09 WO PCT/US2015/049111 patent/WO2016040431A1/en active Application Filing
  • 2015-09-09 US US15/503,906 patent/US10352210B2/en not_active Expired - Fee Related
  • 2015-09-09 EP EP15767650.3A patent/EP3192068A1/en not_active Withdrawn
  • 2015-09-09 CN CN201580048123.5A patent/CN106715849B/zh not_active Expired - Fee Related
  • 2015-09-09 BR BR112017004638A patent/BR112017004638A2/pt active Search and Examination
  • 2015-09-09 JP JP2017513173A patent/JP6625118B2/ja not_active Expired - Fee Related
  • 2015-09-09 KR KR1020177009228A patent/KR20170052629A/ko unknown

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